JPWO2019077778A1 - Eddy current flaw detection method and eddy current flaw detector - Google Patents

Abstract

Ferromagnetism when detecting cracks generated in an inspected body of a steel structure by applying an alternating magnetic field to the inspected body and detecting the magnetic field generated by the eddy current generated in the inspected body with a magnetic sensor. Provided are an eddy current flaw detection method and an eddy current flaw detector for inspecting by reducing the influence of the magnetization signal of the object to be inspected. A magnetic sensor that detects a magnetic field component parallel to the central axis of the applied coil is placed inside the applied coil that applies a magnetic field to the object to be inspected, at a location away from the central axis of the applied coil, and a predetermined frequency is applied to the applied coil. The magnetic field of is generated, and the in-phase component and the imaginary component of the magnetic signal detected and detected by the magnetic sensor are measured. Then, the analysis is performed by subtracting from the in-phase component and the imaginary component measured in advance where there is no defect to be inspected.

Description

The present invention is an eddy current flaw detection method and an eddy current flaw detection method in which a magnetic sensor detects a magnetic field generated by an eddy current generated in an subject to be inspected by applying an alternating magnetic field to the subject to be inspected to detect defects in the inspected object. Regarding the device.

Conventionally, there are an eddy current flaw detection method and a leakage magnetic flux flaw detection method as a method of magnetically inspecting a defect of a metal structure. In particular, the eddy current flaw detection method is a method in which an alternating magnetic field is applied to an object to be inspected by an applied coil to generate an eddy current for inspection. When the object to be inspected has a defect such as a scratch, the eddy current is disturbed and the magnetic field created by the eddy current changes. In the eddy current flaw detection method, this change in the magnetic field is detected by a detection coil, a magnetic sensor, or the like.

In the eddy current flaw detection method, a magnetic field is generally applied to the object to be inspected by using a circular or square application coil having a central axis in a direction perpendicular to the surface of the object to be inspected, that is, in the direction normal to the object to be inspected. It is generating an electric current. This normal direction is the z-axis.

In addition, the detection coil that detects the magnetic field generated by the eddy current generated in the object to be inspected may use the applied coil itself, but it is arranged coaxially with the applied coil separately from the applied coil and has the same normal line. A method of detecting the magnetic field of a component is widely used (see, for example, Non-Patent Document 1).

In addition to this, various arrangements of application coils and detection coils have been reported. For example, a method has been reported in which the central axis of a rectangular detection coil is orthogonal to the central axis of the applied coil and is arranged horizontally with the surface of the object to be inspected for detection (see Patent Document 1). Alternatively, by arranging a part of the wiring of the applied coil as close as possible to the non-inspected body, an eddy current that generates a magnetic field in the same direction as the extension direction of the wiring is generated in the non-inspected body, and this magnetic field is not inspected. A method of detecting with a magnetic sensor provided on the body surface has been reported (see Patent Document 2).

Eddy current flaw detection methods are classified as surface flaw detection methods. The reason is that, in many cases, an alternating magnetic field having a high frequency is used as the alternating magnetic field applied to the object to be inspected. The depth at which the alternating magnetic field enters from the surface of the object to be inspected is frequency-dependent, and this depth is called the epidermis depth.

In order to inspect a deep region from the surface of the inspected object, it is necessary to lower the frequency of the alternating magnetic field applied to the inspected object. On the other hand, the strength of the eddy current also has a frequency characteristic, and when the alternating magnetic field applied to the object to be inspected has a low frequency, the strength of the eddy current is attenuated and the magnetic field generated by the eddy current is also reduced. Further, the detection coil that detects the magnetic field generated by the eddy current also has a frequency characteristic, and the sensitivity decreases when the alternating magnetic field applied to the object to be inspected has a low frequency. On the contrary, it is known that the higher the frequency of the alternating magnetic field applied to the object to be inspected, the higher the sensitivity of the detection coil.

Therefore, a high-frequency alternating magnetic field is used as the alternating magnetic field applied to the object to be inspected, and as a result, the depth of the epidermis must be reduced, and only the surface of the object to be inspected can be inspected.

Therefore, recently, the development of a flaw detection method using a magnetic sensor having a constant magnetic field sensitivity and high sensitivity regardless of the frequency has been advanced instead of the detection coil so that the measurement can be performed even with a low frequency applied magnetic field.

Magnetic sensors used for non-destructive inspection include Hall elements, magnetoresistive elements (MR), magnetic impedance elements (MI), and even more sensitive superconducting quantum interference elements (SQUID). Further, as described above, it has been reported that a coil using a recent superconducting wire can obtain a constant sensitivity even at a low frequency, although a normal coil cannot obtain a sufficient sensitivity at a low frequency (a recent coil using a superconducting wire). For example, see Non-Patent Document 2).

In these magnetic sensors, the direction in which the magnetic field is detected and the physical quantity to be detected differ due to the structure of the element. Hall elements, MR elements, MI elements, SQUIDs, etc. are manufactured using a thin film manufacturing process, and thus can be made extremely small. However, in a Hall element, in order to obtain a large Hall effect, it is necessary to receive a magnetic field on the plane of the sensor chip in the element, and a region having a relatively large area is required, so there is a limit to miniaturization. .. Similarly, in SQUID, since the magnetic flux, that is, the physical quantity obtained by multiplying the magnetic flux density by the area is measured by using the pickup coil, a region having a relatively large area is required, and there is a limit to miniaturization. On the other hand, MR elements and MI elements are sensors that can detect the magnetic flux density at a very small area of the cross-sectional area of the laminated thin film, that is, at one point, and are less affected by miniaturization.

Even in the eddy current flaw detection method using a magnetic sensor that can inspect up to the low frequency region, the magnetic field created by the eddy current is weaker than the strength of the applied magnetic field, so it can be detected by a magnetic sensor with constant sensitivity from low frequencies. Most of the signals to be applied are applied magnetic field components, and the SN is often insufficient.

Therefore, the present inventor attaches a cancel coil to a magnetic sensor arranged coaxially with an applied coil that generates an applied magnetic field in the z-axis direction, and causes the applied magnetic field entering the magnetic sensor to be generated by the cancel coil. The method of detecting the magnetic signal in the z-axis direction from the inspected object is reported (see Patent Document 3).

As described above, the eddy current flaw detection method has been devised in various ways and is widely used for inspecting cracks generated on the surface of the object to be inspected. In particular, when the material of the object to be inspected is a non-magnetic material such as aluminum or copper, only the magnetic field due to eddy current can be detected purely, so it is possible to detect changes in the magnetic field due to eddy current whose distribution is disturbed by cracks. it can. However, in the case of a magnetic material such as steel, not only the magnetic field generated by the eddy current but also the magnetization due to the magnetic field applied to the subject due to the high magnetic permeability characteristics of the magnetic material is caused by this magnetization. There was a problem that the generated magnetic field was detected as a signal.

In order to solve this problem, it is desirable to make the magnetic probe provided with the application coil and the magnetic sensor as small as possible. In particular, when an MR element or MI element is used as the magnetic sensor, the sensor chips constituting the MR element or MI element can be arranged vertically due to the configuration, so that the sensor chip can be arranged vertically. The magnetic probe can be downsized to the extent of the occupied area of the vertically installed sensor chip.

Japanese Unexamined Patent Publication No. 2005-164442 Japanese Unexamined Patent Publication No. 10-239283 Japanese Unexamined Patent Publication No. 2006-030004

Japan Nondestructive Inspection Association, "Eddy Current Testing I", pp.32-43 Y. Matsunaga, R. Isshiki, Y. Nakamura, K. Sakai, T. Kiwa, K. Tsukada, "Application of a HTS coil with a magnetic sensor to nondestructive testing using a low-frequency magnetic field", IEEE Transactions on Applied Superconductivity, vol. 27, 1800304 (2017)

As a dummy inspected body having cracks, a dummy inspected body having a slit-shaped scratch having a width of 1 mm and a length of 30 mm artificially formed on the surface of a steel plate (SM material) having a thickness of 19 mm is used. When line scanning of the magnetic probe is performed across a wound provided on the body, a graph of signal intensity shown in FIG. 10 can be obtained. That is, the signal output from the magnetic probe has a large change in signal strength as it approaches the scratch provided at the position of 15 mm on the horizontal axis in FIG. 10, and the change in signal strength becomes smaller as it moves away from the scratch, and the original The strength is close to the signal strength.

Here, the applied coil constituting the magnetic probe is a coil in which the innermost dimension is a square shape of 2.3 mm × 2.3 mm and has 32 turns, and a tunnel type MR element is used as the magnetic sensor, and a tunnel type MR element is used. Is arranged on the central axis of the application coil. An alternating current of 100 Hz is passed through the applied coil to generate an alternating magnetic field.

As shown in FIG. 10, in the obtained signal, the overall signal strength is large, and the strength change occurs in the signal strength, so that the strength change tends to be unclear. In particular, the overall signal strength is a signal associated with the magnetization of the sample body generated by applying a magnetic field to the sample body which is a ferromagnet. Therefore, when a low frequency magnetic field is applied to reduce the influence of the magnetization of the sample body, the signal of the eddy current generated in the sample body is also small, so that the magnetic field generated by the eddy current can be detected. It has become difficult.

In view of this situation, the present inventor has come up with the present invention while conducting research and development in order to enable more accurate detection of cracks generated in an inspected object.

In the eddy current flaw detection method of the present invention, in the eddy current flaw detection method in which the object to be inspected is inspected by line scanning the object to be inspected with a magnetic probe provided with an applied coil and a magnetic sensor, the magnetic sensor is the center of the applied coil. The magnetic field component parallel to the axis is detected, the in-phase component and the imaginary component are measured from the signal output from the magnetic sensor, and the initially set reference in-phase component and the reference imaginary component are subtracted to obtain the difference in-phase component and the difference imaginary component. , The crack generated in the inspected object is detected by performing the analysis using the difference in-phase component and the difference imaginary component.

Further, the eddy current flaw detection method of the present invention is also characterized in the following points.
(1) The reference in-phase component and the reference imaginary component are the in-phase component and the imaginary component measured in the region where there is no defect in the inspected object, or the in-phase component and the imaginary component arbitrarily set.
(2) The magnetic sensor is placed between the central axis of the applied coil and the coil side.

Further, in the eddy current flaw detector of the present invention, a magnetic probe provided with an application coil and a magnetic sensor, a power source for supplying an AC current to the application coil, and a component for measuring in-phase components and imaginary components from the output signal of the magnetic sensor. In a vortex current flaw detector having a measuring instrument and an analyzer that performs analysis using in-phase components and imaginary components obtained by this component measuring instrument, a magnetic sensor detects a magnetic field component parallel to the central axis of the applied coil. Then, in the analyzer, the initially set reference in-phase component and reference imaginary component are subtracted from the in-phase component and imaginary component obtained by the component measuring instrument to obtain the difference in-phase component and the difference imaginary component, and the difference in-phase component and the difference imaginary component are obtained. Is used for analysis.

Further, the eddy current flaw detector of the present invention is also characterized in the following points.
(1) The reference in-phase component and the reference imaginary component are the in-phase component and the imaginary component measured in the region where there is no defect in the inspected object, or the in-phase component and the imaginary component arbitrarily set.
(2) The magnetic sensor shall be placed between the central axis of the applied coil and the coil side to detect the magnetic field component parallel to the central axis.
(3) A plurality of magnetic sensors are arranged on the magnetic probe.
(4) The magnetic sensors are arranged symmetrically with respect to the plane of symmetry including the central axis of the applied coil.
(5) Attach multiple magnetic probes to the adapter that allows the magnetic probes to be attached and detached.

According to the present invention, the in-phase component and the imaginary component measured in a healthy region without cracks in advance, or the in-phase component and the imaginary component set arbitrarily are subtracted from the measured in-phase component and the imaginary component as initial values. It is possible to reduce the influence of the magnetization signal of the ferromagnet and extract the signal change due to the crack.

It is explanatory drawing of the eddy current flaw detector. It is a graph of the signal strength obtained by the eddy current flaw detection method which concerns on this invention. It is explanatory drawing of the magnetic probe of the eddy current flaw detector which concerns on this invention. It is a graph of the signal intensity obtained by line scanning the dummy inspected object by the eddy current flaw detector according to the present invention. It is explanatory drawing of the magnetic probe of the eddy current flaw detector which concerns on this invention. It is a graph of the signal intensity obtained by line scanning the dummy inspected object by the eddy current flaw detector according to the present invention. It is explanatory drawing of the magnetic probe of the eddy current flaw detector which concerns on this invention. It is a graph of the signal intensity obtained by line scanning the dummy inspected object by the eddy current flaw detector according to the present invention. It is explanatory drawing of the usage form of the magnetic probe of the eddy current flaw detector which concerns on this invention. It is a graph of the signal strength obtained by line scanning a dummy inspected object with a conventional eddy current flaw detector.

As shown in FIG. 1, the eddy current flaw detector of the present invention includes a magnetic probe 2-1 including an application coil and a magnetic sensor, and a magnetic sensor that adjusts a signal output from the magnetic sensor of the magnetic probe 2-1. Analysis using the circuit 5 and the lock-in amplifier 6 as a component measuring instrument for measuring the in-phase component and the imaginary component from the output signal of the magnetic sensor, and the in-phase component and the imaginary component detected by the lock-in amplifier 6. It has a device 7 and a power supply 8 that supplies an AC current to the application coil of the magnetic probe 2-1. The magnetic sensor circuit 5 may be used as a component measuring instrument in combination with the lock-in amplifier 6. In FIG. 1, reference numeral 9 is an inspected object, and for convenience of explanation, the flat inspected object 9 is positioned on the XY plane, and the normal direction of the inspected object 9 is the Z-axis direction. ..

The configuration of the magnetic probe 2-1 will be described in detail later, but the magnetic sensor detects a magnetic field component parallel to the central axis of the applied coil. As the magnetic sensor, a tunnel type MR element, an anisotropic MR element, a giant MR element, an MI element, or the like can be used. In this embodiment, a tunnel type MR element is used. The central axis of the applied coil is parallel to the Z axis.

The power supply 8 that supplies an alternating current to the applied coil inputs information such as the frequency of the supplied alternating current to the lock-in amplifier 6, and the lock-in amplifier 6 starts from the magnetic sensor circuit 5 based on the input information. The input signal is detected and the in-phase component and the imaginary component are measured. Instead of using the lock-in amplifier 6, the analyzer 7 may perform a fast Fourier transform on the output signal of the magnetic sensor circuit 5 to identify in-phase components and imaginary components.

The analyzer 7 is a personal computer in the present embodiment, and the difference in-phase component and the difference imaginary number component are obtained by subtracting the initially set reference in-phase component and the reference imaginary number component from the in-phase component and the imaginary number component obtained by the lock-in amplifier 6. Then, the analysis is performed using the difference in-phase component and the difference imaginary number component.

The initially set reference in-phase component and reference imaginary component are stored in advance in a predetermined storage area of the analyzer 7. As the reference in-phase component and the reference imaginary component, the in-phase component and the imaginary component measured in the region where there is no defect in the inspected object can be used, and the inspected object is set as the initial setting mode at the beginning of the inspection by the eddy current flaw detector. It is possible to measure and set the in-phase component and the imaginary component measured in the region where there is no defect. Alternatively, it may be an arbitrarily set in-phase component and imaginary component.

In the following, the dummy inspected body described in the above-mentioned [Problems to be Solved by the Invention], that is, a steel plate (SM material) having a thickness of 19 mm, is imitated as a crack on the surface of the steel plate. The eddy current flaw detection method of the present invention will be described using a dummy inspected body having a slit-shaped scratch having a width of 1 mm and a length of 30 mm.

When performing line scanning with the magnetic probe of the eddy current flaw detector described above for the dummy object to be inspected, the reference common mode component and the reference imaginary component are initially initialized using the measurement data of the first point of the line scanning. Set. After the initial setting of the reference in-phase component and the reference imaginary number component, the reference in-phase component and the reference imaginary number component are subtracted from the in-phase component and the imaginary number component of the measurement data obtained after that to obtain the difference in-phase component and the difference imaginary number component. The graph of the signal strength obtained by using the difference in-phase component and the difference imaginary component is as shown in FIG.

As shown in FIG. 2, the signal strength increases as it approaches the scratch existing at the position of 15 mm on the horizontal axis of FIG. 2, and the signal returns to the baseline immediately above the scratch. Furthermore, the signal strength increases as the distance from the scratch increases, and then it attenuates and returns to the baseline. By subtracting the reference in-phase component and the reference imaginary component from the measured in-phase component and the reference imaginary component, respectively, the influence of the magnetization signal of the ferromagnet can be reduced and the signal change due to the scratch can be extracted. .. That is, it is possible to reliably detect scratches.

In FIG. 2, the signal change indicating the presence of a scratch is a wide change of about 20 mm, and the signal returns to near the signal strength of the original baseline immediately above the scratch.

When measuring the signal strength from which the graph of FIG. 2 was obtained, the magnetic sensor was arranged on the central axis of the applied coil in the magnetic probe. On the other hand, as shown in FIG. 3, the magnetic sensor was removed from the central axis of the applied coil and placed between the central axis of the applied coil 1-1 and the coil side. The coil side is a part of the coil that constitutes the closed loop.

Here, in the present embodiment, the applied coil 1-1 is arranged on the tip end side of the magnetic probe 2-1 as a coil having a number of turns of 30 and a square shape having an innermost dimension of 7 mm × 2.3 mm. The application coil 1-1 is connected to the power supply 8 via appropriate wiring. The shape of the applied coil 1-1 may be circular or elliptical instead of square, and may have a closed loop shape.

The magnetic sensor 4-1 is a tunnel type MR element in the present embodiment, and is a position away from the central axis of the applied coil 1-1, preferably a distance from the central axis of the applied coil 1-1 to the coil side. It is better to separate by 1/2 or more.

In the present embodiment, the magnetic sensor 4-1 is mounted on the magnetic sensor mounting substrate 3-1 and arranged in the magnetic probe 2-1. In FIG. 3, reference numeral S-1 is a socket for connecting the magnetic sensor mounting board 3-1 and the sensor wiring T-1. The sensor wiring T-1 is connected to the magnetic sensor circuit 5 via appropriate wiring.

FIG. 4 shows a graph of the signal intensity obtained by line scanning the dummy inspected object using the magnetic probe 2-1 having the configuration shown in FIG. Here, the reference in-phase component and the reference imaginary component are initially set using the measurement data of the first point of line scanning. Further, an alternating current of 100 Hz is passed through the applied coil 1-1 to generate an alternating magnetic field.

As shown in FIG. 4, a signal peak was obtained near a scratch existing at a position of 15 mm on the horizontal axis, and the change width could be a sharp signal change of about 5 mm.

The number of magnetic sensors arranged in the application coil of the magnetic probe is not limited to one, but may be multiple. In particular, as shown in FIG. 5, the magnetic sensors 4-2 and 4-3 can be arranged symmetrically with respect to the plane of symmetry including the central axis of the applied coil 1-2.

Here, too, the applied coil 1-2 is arranged on the tip side of the magnetic probe 2-2 as a coil having a number of turns of 30 with the innermost dimension being a square of 7 mm × 2.3 mm. The application coil 1-2 is connected to the power supply 8 via appropriate wiring. The shape of the applied coil 1-2 may be circular or elliptical instead of square, and may have a closed loop shape.

The magnetic sensors 4-2 and 4-3 are tunnel-type MR elements in the present embodiment, and are located away from the central axis of the applied coil 1-2, preferably the coil side from the central axis of the applied coil 1-2. The plane including the central axis of the applied coil 1-2, which is more than 1/2 of the distance to the coil 1-2, is targeted as the plane of symmetry. ing. In this embodiment, the two magnetic sensors 4-2 and 4-3 are separated by about 5 mm.

Also in this embodiment, the magnetic sensors 4-2 and 4-3 are mounted on the magnetic sensor mounting substrates 3-2 and 3-3, respectively, and arranged in the magnetic probe 2-2. In FIG. 5, reference numeral S-2 is a socket for connecting the magnetic sensor mounting board 3-2 and the sensor wiring T-2, and reference numeral S-3 is the magnetic sensor mounting board 3-3 and the sensor wiring T. It is a socket to connect with -3. The sensor wirings T-2 and T-3 are connected to the magnetic sensor circuit 5 via appropriate wirings, respectively.

FIG. 6 shows a graph of the signal strength obtained by line scanning the dummy inspected object using the magnetic probe 2-2 having the configuration shown in FIG. Here, the reference in-phase component and the reference imaginary component are initially set using the measurement data of the first point of line scanning. Further, an alternating current of 100 Hz is passed through the applied coil 1-2 to generate an alternating magnetic field.

As shown in FIG. 6, the two magnetic sensors 4-2 and 4-3 obtained exactly the same results, and one signal peak obtained by a scratch existing at a position of 15 mm on the horizontal axis. Is steep and has a half-value width of about 2.5 mm.

In the present embodiment, the two magnetic sensors 4-2 and 4-3 are separated by about 5 mm, so that the two peaks shown in FIG. 6 are separated by about 5 mm. Since the full width at half maximum is smaller than the distance between the magnetic sensors 4-2 and 4-3, it indicates that cracks can be detected independently when line scanning is performed. This result shows that even if two or more scratches are present close to each other, they can be clearly separated and detected if the half width is 2.5 mm or more apart.

Since the size of the magnetic probe in the eddy current flaw detector of the present invention is restricted by the size of the applied coil, in order to realize a two-channel magnetic probe, one dare to combine one applied coil and one magnetic sensor. As shown in FIG. 5, it is possible to realize a small magnetic probe by forming two channels with one application coil and two magnetic sensors, instead of providing two magnetic sensor probes.

In the magnetic probe 2-2 shown in FIG. 5, the magnetic sensors 4-2 and 4-3 arranged symmetrically with respect to the plane of symmetry including the central axis of the applied coil 1-2 are two magnetic sensors 4-2, The central axis of the applied coil 1-2 is positioned in the middle of 4-3, but as an example of transformation, for example, as shown in FIG. 7, on a plane of symmetry including the central axis of the applied coil 1-3. On the other hand, two magnetic sensors 4-4 and 4-5 may be arranged symmetrically.

Here, the applied coil 1-3 is arranged on the tip side of the magnetic probe 2-3 as a coil having a number of turns of 30 with the innermost dimension being a square of 7 mm × 2.3 mm. The application coils 1-3 are connected to the power supply 8 via appropriate wiring. The shape of the applied coil 1-3 may be circular or elliptical instead of square, and may be in the shape of a closed loop.

The magnetic sensors 4-4 and 4-5 are tunnel-type MR elements in the present embodiment as well, and are located at a position away from the central axis of the applied coil 1-3, preferably a coil from the central axis of the applied coil 1-2. The planes that are more than half the distance to the sides and include the central axis of the applied coils 1-3 are symmetrically arranged. In particular, in the present embodiment, the central axis of the applied coil 1-3 is not arranged between the two magnetic sensors 4-4 and 4-5.

Also in this embodiment, the magnetic sensors 4-4 and 4-5 are mounted on the magnetic sensor mounting substrates 3-4 and 3-5, respectively, and are arranged in the magnetic probe 2-3. In FIG. 7, reference numeral S-4 is a socket for connecting the magnetic sensor mounting board 3-4 and the sensor wiring T-4, and reference numeral S-5 is the magnetic sensor mounting board 3-5 and the sensor wiring T. It is a socket for connecting to -5. The sensor wirings T-4 and T-5 are connected to the magnetic sensor circuit 5 via appropriate wirings, respectively.

FIG. 8 shows a graph of the signal intensity obtained by line scanning the dummy inspected object using the magnetic probes 2-3 having the configuration shown in FIG. 7. In the present embodiment, the two magnetic sensors 4-4, 4-5 are used as the reference in-phase component and the reference imaginary number component instead of using the in-phase component and the imaginary number component obtained from the measurement data of the first point of line scanning. Of these, the reference in-phase component and the reference imaginary component obtained from the other magnetic sensor with respect to one magnetic sensor are defined as the in-phase component and the imaginary component. That is, the difference in-phase component and the difference imaginary number component are measured by subtracting the in-phase component and the imaginary number component of the magnetic signal obtained by each of the magnetic sensors 4-4 and 4-5.

In the magnetic probe 2-3 having the configuration shown in FIG. 7, since the magnetic sensors 4-4 and 4-5 are adjacent to each other, it is possible to measure the difference in-phase component and the difference imaginary component in a manner close to a differential signal. Will be. In particular, there is a feature that magnetic noise, which is a problem when measuring a ferromagnetic material such as a steel plate, is eliminated, and a signal change can be obtained only where there is a defect.

When inspecting by the eddy current flaw detection method using the magnetic probes 2-1, 2-2, 2-3 configured as described above, an appropriate adapter is used so that the line scanning of the magnetic probe can be performed stably. Alternatively, a magnetic probe may be attached to the operation arm for use.

FIG. 10 shows a case where it is used for inspection of a welded portion 13 in which a U rib 12 is welded to a steel slab 11 made of steel used for a road bridge.

In a road bridge, a steel slab 11 made of steel is laid under the pavement surface of the road, and a steel U-rib 12 is welded to the lower surface of the steel slab 11 to form a support structure. When a loaded vehicle frequently passes through a road bridge, cracks are likely to occur in the welded portion 13 that welds the U-rib 12 and the steel deck 11 due to the vibration generated by the load transfer.

Further, since the weld bead in the welded portion 13 has a width, the area of the applied coil provided on the magnetic probe is smaller than the surface of the weld bead with only one magnetic probe, so that line scanning is performed many times. Need to be done.

Therefore, as shown in FIG. 10, a plurality of magnetic probes 2-4, 2-5, 2-6 can be detachably attached to the adapter 10 to which the magnetic probes are mounted, and the plurality of magnetic probes 2-4 can be attached and detached. By line-scanning 2, 2-5, 2-6 at a time, the inspection time can be shortened.

The adapter 10 of the present embodiment has an arc-shaped substrate centered on a welded portion, and magnetic probes 2-4,2-5,2-6 are inserted into the substrate at predetermined intervals in the circumferential direction. A through hole is provided.

Each magnetic probe 2-4,2-5,2-6 can be mounted by simply inserting it into the through hole of the adapter 10, and as shown in FIG. 10, three magnetic probes 2-4,2-5,2 A magnetic probe equipped with -6 and each magnetic probe 2-4, 2-5, 2-6 is shown in FIG. 5 and provided with two magnetic sensors 4-2, 4-3 as in the magnetic probe 2-2. By doing so, a 6-channel magnetic sensor array can be realized.

In the present embodiment, the adapter 10 is made of plastic, and a rolling roller R that rolls in contact with the steel plate 11 or the U rib 12 is provided at the end of the adapter 10, so that the welded portion 13 is formed. It can be easily moved along the stretching direction, and line scanning can be performed stably.

The adapter 10 may have an appropriate shape according to the shape of the inspection location, and can inspect various locations without changing the magnetic probe and the inspection device.

INDUSTRIAL APPLICABILITY The present invention can be widely used for inspections for detecting defects such as cracks in metallic structures by an eddy current flaw detection method, and is particularly difficult for conventional steel structures such as bridges, buildings, and factories. It can be applied to the inspection of structures in a wide range of fields such as plants, power generation equipment, and railways.

1-1 Application coil 1-2 Application coil 1-3 Application coil 2-1 Magnetic probe 2-2 Magnetic probe 2-3 Magnetic probe 2-4 Magnetic probe 2-5 Magnetic probe 2-6 Magnetic probe 3-1 Magnetic sensor Mounting board for 3-2 Mounting board for magnetic sensor 3-3 Mounting board for magnetic sensor 3-4 Mounting board for magnetic sensor 3-5 Mounting board for magnetic sensor 4-1 Magnetic sensor 4-2 Magnetic sensor 4-3 Magnetic sensor 4-4 Magnetic sensor 4-5 Magnetic sensor 5 Magnetic sensor circuit 6 Lock-in amplifier 7 Analyzer 8 AC power supply for exciting coil 9 Inspected object 10 Adapter 11 Steel deck slab 12 U rib 13 Welded part

Claims (9)

In the eddy current flaw detection method in which an object to be inspected is inspected by line scanning the object to be inspected with a magnetic probe provided with an application coil and a magnetic sensor.
The magnetic sensor is determined to detect a magnetic field component parallel to the central axis of the applied coil.
The in-phase component and the imaginary number component are measured from the signal output from the magnetic sensor, and the initially set reference in-phase component and the reference imaginary number component are subtracted to use the difference in-phase component and the difference imaginary number component as the difference in-phase component and the difference imaginary number component. A vortex current flaw detection method that detects cracks generated in the object to be inspected by performing analysis. The eddy current flaw detection according to claim 1, wherein the reference in-phase component and the reference imaginary component are an in-phase component and an imaginary component measured in a region where there is no defect in the inspected object, or an arbitrarily set in-phase component and an imaginary component. Law. The eddy current flaw detection method according to claim 1 or 2, wherein the magnetic sensor is arranged between the central axis of the applied coil and the coil side. A magnetic probe with an application coil and a magnetic sensor,
A power supply that supplies an alternating current to the applied coil,
A component measuring instrument that measures in-phase components and imaginary components from the output signal of the magnetic sensor,
An analyzer that performs analysis using the in-phase component and the imaginary component obtained by this component measuring instrument, and
In an eddy current flaw detector with
The magnetic sensor detects a magnetic field component parallel to the central axis of the applied coil.
In the analyzer, the initially set reference in-phase component and reference imaginary component are subtracted from the in-phase component and imaginary component obtained by the component measuring instrument to obtain a difference in-phase component and a difference imaginary component, and the difference in-phase component and the difference imaginary component are obtained. An eddy current flaw detector that analyzes using. The eddy current flaw detection according to claim 4, wherein the reference in-phase component and the reference imaginary component are an in-phase component and an imaginary component measured in a region where there is no defect in the inspected object, or an arbitrarily set in-phase component and an imaginary component. apparatus. The eddy current flaw detector according to claim 4 or 5, wherein the magnetic sensor is arranged between the central axis of the applied coil and the coil side to detect a magnetic field component parallel to the central axis. The eddy current flaw detector according to any one of claims 4 to 6, wherein a plurality of the magnetic sensors are arranged on the magnetic probe. The eddy current flaw detector according to claim 7, wherein the magnetic sensor is arranged symmetrically with respect to a plane of symmetry including the central axis of the applied coil. The eddy current flaw detector according to any one of claims 4 to 8, further comprising a plurality of the magnetic probes, the eddy current flaw detector having an adapter to which the magnetic probe can be detachably attached.

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